Numerical Investigation of Cooling Holes Injection to Highly-Diffusive Endwalls for RDC applications.

Recent trends in aeroengine developments aim at developing high thrust, low emission engines based on innovative concepts. Amongst them, the use of pressure gain combustion should ensure that cycle efficiency will raise by 17%, at least for low compression ratios (e.g., short-haul flights, helicopters). Such a remarkable increase entails a significative reduction in pollutant emissions, which reduces to net zero if hydrogen is considered as energy carrier (not considering NOx emissions). An interesting way to realize the Zeldovich-Neumann-Doring cycle includes the usage of a rotating detonation combustor. The resulting outflow of this unconventional machine is characterized by a high frequency fluctuation of temperature, flow angle and Mach number. The peculiar inlet boundary condition associated to a rotating detonation combustor obliges designers to take into consideration at least two technical problems when the coupling with high-pressure turbine is realized: first, a transition duct that reduces flow fluctuations and mean Mach number (at least below a value of 0.6) must be designed to couple the two components. Second, the duct and the turbine must be heavily cooled, but the pulsating pressure value makes the cooling mass-flow unsteady. Moreover, in such a configuration the development of secondary flows (i.e., the horseshoe vortex) is highly amplified, thus generating losses and off-design conditions that prevent any real cycle efficiency augmentation. The MSc thesis project is hence focused on enabling technologies for pressure gain combustion cycles. In detail, the performance of a limited array of holes subject to unsteady boundary conditions is analyzed in terms of adiabatic effectiveness and heat transfer coefficient, also including its ability to weaken the formation of secondary flows at the turbine inlet. To do so, an already designed shape for the final part of the transition duct is used to mimic the presence of an already weakened peak flow pulsation at a Mach=0.6 level. The process involves an initial phase of steady simulations using RANS equations, which are subsequently employed in the second phase as the initial conditions for unsteady simulations utilizing URANS equations. The simulations are conducted within the ANSYS FLUENT environment. All the relevant non-dimensional parameters are kept at engine-representative scale, thus allowing for extrapolating information on the performance of the holes if subject to pulsating conditions.